Since the disclosure of fluorocarbon polymers containing sulfonic acid groups (U.S. Pat. No. 3,282,875) considerable progress has been made in adapting these polymers for use as a membrane in electrochemical cells and chemical reactors. Most of this work has dealt with the electrolytic production of chlorine, and caustic soda, and the nitration, sulfonation and alkylation of hydrocarbons. In these and similar applications, the membranes are used to separate fluids under pressure at operating temperature in corrosive, oxidizing chemical environments. For the production of chlorine and caustic soda, flat sheets of the membrane are pressure sealed between plastic or metal frames to form compartments in the electrolytic cell that separate the anolyte and catholyte fluids. In cylindrical electrolytic cells, tubes of a membrane are used to separate the anolyte and catholyte fluids, wherein the ends of the tubes must be closed to effect separation of the fluids and the anodic and cathodic electrical potentials. The components of the closure of the membrane tubes must be stable to the normally corrosive chemical environment at operating temperature, pressure and electrical potentials.
Perfluorocarbon sulfonic acid membranes are sold in sheet form with and without fabric reinforcement. The membrane sheets range in thickness from about 0.004 inches to 0.020 inches (Edward H. Price. The Commercialization of Ion Exchange Membranes to Produce Chlorine and Caustic Soda, 152nd National Meeting Electrochemical Society, Atlanta, Ga. October 1977). The sheets can be formed into tubes by heat sealing together two edges of the sheet which results in a cylindrical tube with a seam approximately twice the thickness of the initial sheet. The membranes absorb water and polar organic materials from about 5 to 70% of dry weight which results in large dimensional changes on hydration, solvation and drying. Fabric reinforced membranes are used to reduce dimensional changes and to improve mechanical properties but still show substantial dimension changes upon hydration under operating conditions.
Thin wall plastic tubes are not generally used to separate fluids in chemical and electrolytic processes. Heretofore, there has been no satisfactory methods for closing the ends of perfluorocarbon and other plastic tubes for use in electrolytic cells and fluid-flow reactors. Elastomeric rubber and thick wall plastic tubes are generally connected to pipes and other cylindrical headers with metal type hose clamps wherein the plastic tube is deformed to accommodate the out-of-round configuration of the clamp. The thin wall and low elasticity of the perfluorocarbon and most other plastic tubes, especially with fabric reinforcement, preclude the use of ring clamps to effect a fluid tight seal of the plastic tube to a cylindrical header. The corrosive and electrical environments, also, essentially preclude the use of metal rings and clamps. Glues and sealants can be used to connect plastic tubes to cylindrical pipes and headers. However, the large dimensional changes of perfluorocarbon membranes on hydration and solvation and the corrosive environment make glue and sealant connections unreliable or unusable. A conical header and tapered ring with tie bolts and clamps can be used to compress an elastomeric O ring on the surface of a plastic tube to effect a fluid tight connection. With corrosive and oxidizing environments the O ring usually fails in a short period with loss of compartmentation of fluids. A conical header and tapered ring assembly does not accommodate close spacing of electrodes in electrolytic cells and close spacing of plastic tubes in chemical reactors.
An object of the instant invention is to provide a method and apparatus for connecting thin wall perfluorocarbon membranes and other plastic tubes to a cylindrical header that forms a fluids tight connection suitable for pressure operation in corrosive and oxidizing environments at elevated temperatures that accommodates dimensional changes of the plastic tube and hydration, solvation and drying, permits close spacing of electrodes in electrolytic cells and chemical reactors and is easily made and removed to facilitate maintenance and repair.